Seminar 20: Communication & homeostasis Flashcards
(27 cards)
Define Homeostasis:
the ability for an organism to maintain a stable internal environment despite fluctuations in their external environment
Why is homeostasis important for living things:
Disruption to internal conditions can lead to death as certain functions cannot be carried out.
Desc an example of negative feedback:
Increase in blood glucose levels
- The pancreas releases insulin, triggering glucose uptake by liver cells which decreases blood glucose.
- When levels are restored, pancreas stops insulin production
Desc an example of positive feedback:
Blood clotting
- Cut in the blood vessel wall triggers nearby platelet to release chemical signals which activate clotting factors & attract platelets to site of injury (initiates blood clot)
- Platelets release chemicals that increase platelet > injury until clot seals off wound
What is intercellular cell signalling?
Communication b/w cells, 1 cell secretes ligand which induces a response in the targeted cells
What is intracellular cell signalling?
Binding on ligand > receptor, causing signal processing w/in a cell
What is contact dependent cell signalling?
Communication b/w physically linked cells (ligands pass via gap junctions or plasmodesmata)
What is synaptic cell signalling?
Communication used by cells of the nervous system
Why are gap junctions & plasmodesmata important in cell signalling?
They allow adjacently linked cells to communicate via contact-dependent signalling as ligands flow through them from cell to cell
Where is insulin synthesised?
Pancreas - Beta islets of Langerhans
Where is Glucagon synthesised?
Pancreas - Alpha islets of Langerhans
Target cells of insulin, what func is induced?
Liver - induces uptake of glucose & storage of it into glycogen
Target cells of glucagon, what func is induced?
Liver - induces breakdown of glycogen into glucose
Effects of insulin binding to liver cells in order: (4)
- Auto phosphorylation of insulin receptor, initiating a signalling pathway
- Increases # of glucose transporters in the membrane (increased facilitated diffusion of glucose into the cell)
- Glucokinase activated (prevents glucose from exiting cell as it inhibits activity of glucose phosphatase)
- Activates enzyme (glycogen synthase) that converts glucose > glycogen
Effects of glucagon binding to liver cells in order: (3)
- Glucagon G protein coupled receptor activates glycogen phosphorylase (breaks glycogen into monomers of glucose)
- Glycogen synthase inhibited (prevents reformation of glycogen)
- Leads to reduction of stored glycogen in the liver & release of glucose
How are blood glucose levels elevated by glucagon binding to receptors on liver cells? (2)
- As less insulin is present: enzymes that remove phosphate phosphate grps from glucose are elevated, so glucose from breakdown of glycogen can be diffused out of the cell.
- Blood glucose levels are elevated
Plant vs Animal hormones, compare: (3)
- Both can vary the conc of molecules & act at a distance.
- Animal hormones tend to be produced by specific glands/cells & tend to have specific effects
- Plant hormones can be synthesised in many locations & play multiple regulatory roles
Action potential is …
the specific change in charge across the cell membrane, allowing electrical signals to be propagated in the nervous system
Resting membrane potential is…
the difference of membrane potential b/w inside & outside of the cell membrane of neurons @ rest (when they’re not being stimulated)
- level when membrane potential isn’t hyperpolarized or depolarised, no signals (-70 mV)
When will depolarisation occur?
Depolarised when Na+ channels open, allowing Na+ to enter cell down its conc gradient
When will hyperpolarization occur?
when K+ channels open, K+ flows out of cell down the conc gradient which reduces the membrane potential
Refractory period reduces the chances of …
another action potential occurring until the resting potential is achieved again
How is the K+/Na+ conc gradient created when the neuron is at rest?
- K+ channels are the main type of channels open at rest
- Sodium/Potassium pump uses energy to continuously move Na+ out & K+ in (creates conc gradient)
What happens when the voltage Ca2+ channels open? (6)
- Ca2+ enters the presynaptic neuron
- Triggers fusion of vesicles w/ neurotransmitters
- Neurotransmitters exit via exocytosis to the synaptic cleft
- Neurotransmitters bind to receptors on postsynaptic neuron
- Results in increase or decrease in postsynaptic membrane potential
- EFFECT: changes the likelihood of an action potential occurring in the postsynaptic cell (either increase it or decrease
